1. Field of the Invention
The present invention relates to an electrophotographic image forming apparatus such as a copier, printer, or facsimile apparatus, and more particularly to an image forming apparatus that is provided with a function for preventing the rusting of metallic components, preventing paper jams, and improving the cooling capability of a heat pipe by ensuring that water droplets do not become adhered to the heat pipe, thereby reducing thermal resistance.
2. Description of the Background Art
In recent years, an increase in the number of mechanical constitutional components in an electrophotographic image forming apparatus such as a copier has been caused by increased functionality resulting from increased speed, digitalization, and colorization. This has led to an increase in heat-generating members which generate heat, such as a polygon motor and a hard disk, while the overall size of the apparatus main body shows a decreasing trend. As a result, the amount of space between components must be reduced relatively, causing an increase in heat generation density. It is therefore becoming more and more important to provide measures against the effects of heat inside the apparatus, and to develop cooling techniques that can be applied within a restricted space. Moreover, with this increase in heat density, the moisture contained in paper is evaporated by the fixing apparatus, and water generated within the apparatus may cause rusting of the metallic components and jams when the water falls onto the paper. Therefore, measures against water vapor inside the apparatus must also be taken.
As an example of the prior art relating to these problems, Japanese Unexamined Patent Application Publication 2003-91189 (abbreviated to Prior Art Reference 1 hereafter) discloses an image forming apparatus comprising an imaging apparatus which forms a toner image on a photosensitive body and then transfers the toner image onto a sheet of paper, and a fixing apparatus provided in the vicinity of the imaging apparatus for fixing the toner image transferred onto the paper by means of heat. A heat shielding plate and a heat pipe are disposed between the imaging apparatus and fixing apparatus, a heat radiating fin is disposed at one end of the heat pipe, and a fan is provided for forcibly cooling the heat radiating fin.
Further, Japanese Unexamined Patent Application Publication 2002-091105 (abbreviated to Prior Art Reference 2 hereafter) discloses an image forming apparatus provided with a mechanism for discharging water vapor generated in the apparatus to the outside of the apparatus using the surface of thermal insulation means (a thermal insulation member 5a) as an inner wall of a duct (ventilation duct 4b) (see FIGS. 5, 6).
Further, Japanese Unexamined Patent Application Publication H9-325671 (abbreviated to Prior Art Reference 3 hereafter) discloses an electrophotographic apparatus in which the operation of an exhaust fan (a fan 42 in the document) is controlled in accordance with a humidity value (when the absolute humidity reaches or exceeds 20 g/m3, the fan 42 is rotated in reverse to discharge air from the apparatus main body).
Further, Japanese Unexamined Patent Application Publication 2000-259064 (abbreviated to Prior Art Reference 4 hereafter) discloses a heat discharge apparatus in which a duct is provided so as to pass between a heat source portion for discharging heat and an affected portion that is affected by the heat, an exhaust port of the duct is opened onto the upper portion of the apparatus, and intake ports are opened on both sides of the heat source portion in lower positions than the exhaust port. Moreover, a thermal insulation member is provided on an outer casing part of the heat source portion on the side facing the affected portion, and a communicative port which connects the interior space of the duct to the space in the vicinity of the heat source portion is provided on the route of the duct on the opposite side of the thermal insulation member.
Further, Japanese Unexamined Patent Application Publication H11-338331 (abbreviated to Prior Art Reference 5 hereafter) discloses a heat shielding apparatus for preventing the transfer of the heat from a heat source portion inside an image forming apparatus to a portion to be protected, in which a ventilating duct having an exhaust port on the upper side of the heat source portion and an intake port on the lower side of the exhaust port is provided between the heat source portion and the portion to be protected, a thermal insulation portion is provided on the side of the heat source portion between the heat source portion and the ventilating duct, and a heat radiating portion is provided on the side of the ventilating duct between the heat source portion and the ventilating duct.
Further, Japanese Unexamined Patent Application Publication 2001-013855 (abbreviated to Prior Art Reference 6 hereafter) discloses an image forming apparatus for recording an image on a sheet of paper using an image recording portion, inserting the recorded paper into a fixing apparatus, and fixing the recorded image. A cooling duct is disposed between the image recording portion and the fixing apparatus so as to shield the image recording portion and fixing apparatus from each other, a temperature sensor is provided inside the cooling duct, and when the temperature sensor detects that the temperature inside the cooling duct has reached a predetermined temperature, an axial fan is operated so that air is introduced into the cooling duct.
Further, Japanese Unexamined Patent Application Publication 2000-231293 (abbreviated to Prior Art Reference 7 hereafter) discloses an image forming apparatus comprising image forming means for forming an image on a sheet of paper, fixing means for heat-fixing the image formed on the paper by the image forming means, a paper conveyance path for conveying the paper subjected to heat-fixing by the fixing means to a paper discharge portion, and a water absorbing member provided in the vicinity of the paper conveyance path for absorbing moisture and drying the paper conveyance path.
Further, Japanese Unexamined Patent Application Publication 2002-366010 (abbreviated to Prior Art Reference 8 hereafter) discloses an image forming apparatus comprising one or a plurality of image carriers, one or a plurality of image forming means for forming a toner image on the image carrier, transfer means for transferring the toner image forming on the image carrier to a recording medium directly or via an intermediate transfer body, fixing means constituted by a fixing roller, heating means for heating the fixing roller, and roller temperature detecting means for detecting the temperature of the fixing roller, the heating means being controlled on the basis of the output of the roller temperature detecting means, exhaust means for discharging air in the apparatus to the outside of the apparatus, means for detecting the temperature and humidity on the outside of the apparatus, and means for detecting the temperature and humidity on the inside of the apparatus. The apparatus has a first standby mode in which the heating means and exhaust means are operated, and a second standby mode in which the heating means are operated but the exhaust means are halted, and switches between the first standby mode and second standby mode in accordance with the difference between the detected humidity and temperature on the inside and outside of the apparatus.
With the technique disclosed in Prior Art Reference 1, thermal insulation is provided by the heat shielding plate, thereby preventing rusting of the metallic components and paper jams caused by water vapor, and the heat shielding plate is cooled by the heat pipe and so on, leading to an improvement in the thermal insulation effect. However, with this technique, rusting of the metallic components may occur when water vapor generated as paper passes through the fixing apparatus adheres to the heat pipe, and paper jams may occur when water falls onto the paper.
The techniques disclosed in Prior Art References 4 to 8 are effective in dealing with heat and water vapor inside the respective apparatuses, but under the current circumstances described above, in which the space between components is small, causing an increase in heat generation density, it is impossible to discharge sufficient water vapor from the apparatus with these techniques when the apparatus is operated continuously for a long time period. Therefore, these techniques are not able to sufficiently solve the problems described above relating to rusting of the metallic components and paper jams caused by moisture.
As well as the aforementioned problems in the prior art, when water vapor that is generated as paper passes through the fixing apparatus adheres to the heat pipe, thermal resistance from the outside is generated in the heat pipe, leading to a reduction in the cooling capability of the heat pipe.